1. Field of the Invention
The present invention relates to a lens apparatus, and more specifically, to an impact-resistant structure of a movable barrel member in a lens apparatus applied to an image pickup apparatus such as a camera.
2. Description of the Related Art
Conventionally, image pickup apparatuses such as cameras, for example, digital cameras and video cameras, have been generally commercialized and become widespread, which are configured to sequentially convert an optical image formed by an image pickup optical system to an image signal using a photoelectric conversion element or the like, record the image signal obtained in a recording medium as image data in a predetermined format, and include an image display apparatus such as a liquid crystal display apparatus (LCD) that reproduces and displays the image data recorded in the recording medium as an image.
Image pickup apparatuses of this type are generally provided with a lens apparatus including an image pickup optical system for forming an optical image of an object on a light receiving surface of an image pickup device such as a photoelectric conversion element. This lens apparatus is configured by including an image pickup optical system made up of a plurality of optical lenses or the like and a lens holding barrel member that holds the respective optical lenses in group units, with a predetermined optical lens (and a plurality of lens holding barrel members that hold the optical lens) among the plurality of optical lenses being configured to be able to move in a direction along an optical axis to realize, for example, auto focus operation and variable power operation (zoom operation). Here, the optical lens provided so as to be movable in the direction along the optical axis is called a “movable lens” and the barrel member that holds this movable lens is called a “movable lens holding barrel member.”
As lens apparatuses applied to conventional image pickup apparatuses, various types of lens apparatuses are proposed and commercialized which are provided with a movable lens holding barrel member pivotably supported by a hanger shaft provided parallel to the direction along the optical axis so as to be movable in the same direction, with the movable lens holding barrel member being structured to be movable in the optical axis direction by a nut member that moves in a direction along the optical axis by receiving a drive force from a drive source such as a separately provided motor.
The conventional image pickup apparatus using a lens apparatus having a movable lens holding barrel in such a configuration may be dropped onto a floor or ground or the like during use. In this case, due to an impact by the drop or the like, the movable lens holding barrel may move along the hanger shaft and collide with an internal structure, causing damage to the lens apparatus.
Examples of basic measures for reinforcing resistance against such a drop impact or the like include increasing a thickness of parts and changing a material to improve resistance of parts.
However, the above means of improving the resistance of the parts involves problems such as an increase in manufacturing cost, upsizing of the apparatus itself accompanied by upsizing of the parts and increases of weights of the parts. When weights of the movable lens holding barrel parts increase, there arises a problem that when the parts receive a drop impact or the like, rotation moment centered on the hanger shaft causes stress concentration, which may cause the parts to be more likely to be damaged with cracks or the like.
On the other hand, means disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2007-114707 adopts a two-body structure for a lens holding barrel which is a driven barrel, interposes a spring between both members and causes the two members constituting the driven barrel to engage with each other as one body by an urging force thereof.
Upon receiving a drop impact or the like, such a configuration causes the two members of the driven barrel to be disengaged from each other against the urging force of the spring, and thereby obtains an effect that damage to the driven barrel can be prevented.
However, upon receiving a drop impact or the like, the means disclosed in Japanese Patent Application Laid-Open Publication No. 2007-114707 above may fail to disengage the engagement between the two members constituting the driven barrel depending on the direction in which the impact is applied. In such a case, the impact received may not be alleviated and may be transmitted directly to the driven barrel, causing damage to the members. Furthermore, when an impact as large as exceeding the urging force of the spring is received, there arises a problem that the impact received may be directly transmitted to the driven barrel, causing damage to the members in a similar manner. Moreover, no description is given about sequentially alleviating the impact transmitted to the driven barrel.